The Wizarding World was a place of secrets - from the very beginning it had been so. Held apart from the rest of the world, their existence was kept a secret from those who would harm them; those who, though they held no magic of their own, were so many in number as to overwhelm the few wizards and witches who hid from them.
There was another knowledge beneath that, however; the knowledge that they could, with time and a concentration of their abilities, wipe this danger from the face of the planet. They held the power, if they were but willing to use it; the power to kill, to utterly destroy that which frightened them so. It was this knowledge that many feared more than death itself - that they held within themselves this ability to destroy.
So they kept it a secret, even from themselves. Those who understood just how far their magic could go toward the destruction of all which was beautiful guarded this knowledge, lest those whose moral scruples were few in number become aware.
Laws were passed, banning the use of certain spells, and then later entire groups of spells. Entire branches of knowledge were banned throughout the whole of the wizarding world - a practice which was to continue as territories were laid out in the Muggle world and countries were formed, separating wizards from one another through cultural, political, and geographical lines.
Secrets ruled the WIzarding World. Secrets kept the populace safe in their ignorance, willing to accept, as a whole, the limitations placed upon them by their government, both old and new.
So years passed in ignorance and silence, with little changing in the Wizarding World from the time of Merlin, that man that so many looked up to. A man who had been integral in creating many of the limitations which the Wizarding World now accepted. Change was slow in coming, and was fought by the general populace with a ferocity they showed for little else.
That status quo was almost sacred by the time Harry Potter was born. Lord Voldemort was hated and feared for challenging this status quo - perhaps even more so than for the deaths which had come about at his hands and the hands of his followers. To challenge a world of secrets, to bring knowledge to the forefront with little to no fear of the consequences of chasing such knowledge and power ...
That which the Wizarding World did not understand, they feared. In this respect, they were no different from the muggles which they hid themselves from. And the power which Tom Riddle - Lord Voldemort - held at his fingertips was no different. They did not understand it, but they did understand that it was forbidden to chase such secrets, such knowledge.
Secrets were funny things; you could keep them without ever wondering why. They could be kept from you, without you ever realizing there was more to the world than what you had been told. When an entire society had been taught to ignore a part of their own existence - when they had been systematically taught to keep those same secrets from their own children ... well, those were the sorts of secrets that could prove truly deadly.